Typically, vehicles that use LPG for fuel are configured in a way so that the LPG is injected to the engine in a gas state. LPG is provided from the fuel tank and is turned into gas by being passed through a vaporizer and mixer. However, the LPG engine has drawbacks in that the engine output performance, fuel economy, vehicle start at a low temperature, exhaust gas, and the like are compromised. Therefore, LPI engine vehicles have been under development recently to facilitate increased use.
LPI engine vehicles are configured to compressively transmit LPG fuel to an injector through the fuel line by using a fuel pump installed in the fuel tank. Next, the injector injects fuel into the engine in a liquid state to improve engine output, fuel economy, vehicle start function at a low temperature, and to decrease exhaust gas. In LPI engine vehicles, a shut off valve is equipped in the fuel tank and regulator, respectively. If the LPG switch is turned off while the engine is running, an Interface Box (IFB) closes the shut off valves and stops the fuel flow through the injector.
In the conventional LPI engine vehicles, when the LPG switch is turned off, the isolating valves in the fuel tank and regulator are closed to stop the fuel supply. However, there is a drawback in that even when the engine stops, the fuel pump is continuously activated by another power source, thereby increasing noise and output consumption due to the unnecessary operation of the fuel pump.